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Subelement T8
Modulation modes: amateur satellite operation; operating activities; non-voice and digital communications
Section T8D
Non-voice and digital communications: image signals; digital modes; CW; packet radio; PSK31; APRS; error detection and correction; NTSC; amateur radio networking; Digital Mobile/Migration Radio
Which of the following is a digital communications mode?
  • Packet radio
  • IEEE 802.11
  • JT65
  • All of these choices are correct

Digital communications methods are methods that send digital information (encoded in bits, 0 or 1) instead of sending an analog signal, such as voice or video.

The methods listed here are all digital modes:

  • Packet Radio is probably the best known digital mode which can be thought of as using a modem over a radio to allow computers to exchange data

  • PSK31 is short for Phase Shift Keying, 31 Baud and is more of system for chat over radio; it allows realtime keyboard to keyboad informal chat between operators.

  • MFSK is short for Multiple frequency-shift keying and is a variation of FSK, a method used by some packet radio systems.

  • IEEE 802.11 is a set of specifications for implementing wireless local area network (WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands.

Last edited by gnarly79. Register to edit

Tags: digital modes arrl chapter 5 arrl module 12

What does the term “APRS” mean?
  • Automatic Packet Reporting System
  • Associated Public Radio Station
  • Auto Planning Radio Set-up
  • Advanced Polar Radio System

APRS, Automatic Packet Reporting System, is a standard utilizing packet radio and a GPS to send beacons with the location of the unit. There are many things you can do with APRS, but many use it on bicycles to track their progress, on their vehicle to track where it is, etc. There have even been reports of APRS- equipped vehicles being stolen and then quickly tracked down thanks to the APRS unit.

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Tags: digital modes definitions arrl chapter 5 arrl module 12

Which of the following devices is used to provide data to the transmitter when sending automatic position reports from a mobile amateur radio station?
  • The vehicle speedometer
  • A WWV receiver
  • A connection to a broadcast FM sub-carrier receiver
  • A Global Positioning System receiver

Automatic location reports need to know the location to automatically report; thus, they use a GPS just like anything else would =]

If you think about this one, it couldn't be the speedometer anyway; that would only tell you how fast you are going. (also APRS, Automatic Position Reporting System, can be used when biking, driving, walking, etc all just as easily as the other). The other two options are just random things thrown in hoping you won't know what they are so you'll guess wrong. Nearly everyone knows what a GPS is, so this shouldn't be hard to remember.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: digital modes arrl chapter 5 arrl module 12

What type of transmission is indicated by the term "NTSC?"
  • A Normal Transmission mode in Static Circuit
  • A special mode for earth satellite uplink
  • An analog fast scan color TV signal
  • A frame compression scheme for TV signals

If you ask a broadcast engineer, NTSC stands for Never The Same Color, because his job is to keep all the cameras looking the same. Now that TV is in the Digital Age the only people you see using the NTSC broadcast standard are Amateur Radio Operators.

Actually, NTSC stands for National Television Systems Committee. They created the rules that governed what the broadcast signal would be electronically so every TV would be able to display the correct picture. And what all this has to do with analog fast scan color TV signals, no one really knows.

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Tags: amateur television (atv) arrl chapter 6 arrl module 14

Which of the following is an application of APRS (Automatic Packet Reporting System)?
  • Providing real-time tactical digital communications in conjunction with a map showing the locations of stations
  • Showing automatically the number of packets transmitted via PACTOR during a specific time interval
  • Providing voice over internet connection between repeaters
  • Providing information on the number of stations signed into a repeater

It helps to know what APRS is and does. It transmits a station's GPS coordinates, so other stations can locate it. The components are a GPS receiver, a ham radio transmitter, and some logic to connect the two so the transmitter sends out the GPS coordinates. So:

It has nothing to do with counting packets, It doesn't require voice over Internet, and It doesn't count stations connected to a repeater.

It just provides real time communications that gives your location. In conjunction with a map, it shows your location to the stations that receive your GPS coordinates via the APRS system.

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Tags: aprs digital modes packet radio arrl chapter 5 arrl module 12

What does the abbreviation "PSK" mean?
  • Pulse Shift Keying
  • Phase Shift Keying
  • Packet Short Keying
  • Phased Slide Keying

Phase Shift Keying is a method for digitally transmitting data (with a computer of some sort) by varying (keying) the phase of the signal. Phase refers to where you are in the cycle (the peaks and valleys of the sine wave)

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Tags: digital modes definitions arrl chapter 5 arrl module 12

Which of the following best describes DMR (Digital Mobile Radio)?
  • A technique for time-multiplexing two digital voice signals on a single 12.5 kHz repeater channel
  • An automatic position tracking mode for FM mobiles communicating through repeaters
  • An automatic computer logging technique for hands-off logging when communicating while operating a vehicle
  • A digital technique for transmitting on two repeater inputs simultaneously for automatic error correction

DMR is one of several digital modes. It's the only one that uses time-multiplexing to allow two digital voice signals to be repeated through the same repeater, using the same 12.5 kHz repeater channel.

It's not a position tracking system.

It's not a logging technique.

The third distractor is tempting, because it talks about two simultaneous repeater inputs, but the part about time-multiplexing is unique to DMR, so the best answer.

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Tags: digital modes arrl chapter 6 arrl module 15

Which of the following may be included in packet transmissions?
  • A check sum that permits error detection
  • A header that contains the call sign of the station to which the information is being sent
  • Automatic repeat request in case of error
  • All of these choices are correct

A checksum is an error detection method used by many data transmission types including packet radio. Basically all bytes in the message are added (summed) up and sent as a "checksum". The receiving station repeates this process and "checks" the result against the checksum it received from the sending station.

If the checksum fails (the sums don't match) then an automatic repeat request is sent.

Since packet radio is a form of amateur radio communications the destination station is generally identified at least by call sign, so that information is often included in the header as well.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: digital modes packet radio arrl chapter 5 arrl module 12

What code is used when sending CW in the amateur bands?
  • Baudot
  • Hamming
  • International Morse
  • All of these choices are correct

CW stands for "Continuous Wave", which is a sine wave: an electromagnetic wave of constant amplitude and frequency.

This wave can be interrupted, creating an "off" state. The on and off states can be used to transmit Morse code.

The original version of Morse code developed by Samuel Morse is often referred to as Railroad Morse code or American Morse code—American because the rest of the world adopted International Morse. Eventually International Morse also replaced Railroad Morse in America, and this is what we use today.

The term CW comes up a lot; whether you remember what CW stands for or not, every amateur radio operator should know that CW means Morse code.

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Tags: morse code arrl chapter 5 arrl module 12

Which of the following operating activities is supported by digital mode software in the WSJT suite?
  • Moonbounce or Earth-Moon-Earth
  • Weak-signal propagation beacons
  • Meteor scatter
  • All of these choices are correct

WSJT is software that facilitates short, quick digital transmissions and is very useful for weak signals.

As such, it's great for moonbounce (Earth-Moon-Earth), weak signal beacons and meteor scatter, all of which result in very little of the transmitted signal reaching anyone's receiver.

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Tags: digital modes arrl chapter 5 arrl module 12

What is an ARQ transmission system?
  • A special transmission format limited to video signals
  • A system used to encrypt command signals to an amateur radio satellite
  • A digital scheme whereby the receiving station detects errors and sends a request to the sending station to retransmit the information
  • A method of compressing the data in a message so more information can be sent in a shorter time

ARQ stands for Automatic Repeat reQuest

When the receiving station detects an error, it automatically sends a repeat request to the sending station.

It has nothing to do with encryption (which would be illegal except for sending commands to a satellite), or video signals, or data compression. Indeed, it takes a long time to have the receiving station send a repeat request and to then re-transmit the message, or portion of the message.

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Tags: digital modes arrl chapter 5 arrl module 12

Which of the following best describes Broadband-Hamnet(TM), also referred to as a high-speed multi-media network?
  • An amateur-radio-based data network using commercial Wi-Fi gear with modified firmware
  • A wide-bandwidth digital voice mode employing DRM protocols
  • A satellite communications network using modified commercial satellite TV hardware
  • An internet linking protocol used to network repeaters

Broadband-Hamnet™ was at one time called HSMM-Mesh™ and is one of a couple of different projects which are basically intended to create a peer to peer wireless network on ham radio frequencies.

The first iteration of this involved using the Linksys WRT-54G -- a highly modifiable consumer access point -- with custom firmware on 2.4ghz channel 1, which is actually part of the ham radio allotted spectrum. The idea is that "mesh nodes" can connect to each other automatically and route traffic between each other, thus providing a wireless network which covers a city (or larger) by creating interlinking nodes.

In practice this is more difficult than you might expect, due to congestion on 2.4ghz frequencies, but the project has expanded to include support for other access points and bands as well. There are some offshoots of the project, including AREDN (Amateur Radio Emergency Data Network) and HamWan.

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Tags: digital modes arrl chapter 5 arrl module 12

What is FT8?
  • A wideband FM voice mode
  • A digital mode capable of operating in low signal-to-noise conditions that transmits on 15-second intervals
  • An eight channel multiplex mode for FM repeaters
  • A digital slow scan TV mode with forward error correction and automatic color compensation

FT8 is a relatively new digital mode which became popular in 2017; it very quickly largely replaced JT65 because it's much faster. FT8 is usually used on HF bands and it can achieve very long distances because it is extremely tolerant of noise and interference. It requires that both transmitter and receivers synchronize their computer time with the same time source (which is easy with the internet).

When you transmit, you transmit for 15 seconds and send only a very short (75 bit) message with a 12 bit checksum.

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Tags: digital modes arrl chapter 5 arrl module 12

What is an electronic keyer?
  • A device for switching antennas from transmit to receive
  • A device for voice activated switching from receive to transmit
  • A device that assists in manual sending of Morse code
  • An interlock to prevent unauthorized use of a radio

An electronic keyer is the modern fancy replacement for the traditional telegraph key, or in other words a device that assists in manual sending of Morse code.

Electronic keyers can have a variety of functions including:

  • Separate keys for sending dots and dashes at a specified rate.
  • The ability to set a limited transmission rate (in WPM) while allowing the operator to "get ahead" of the current transmission by buffering up additional code or word spaces to be sent in sequence after previously entered code is sent.
  • The ability to continually send dots or dashes by holding down a key so that fewer hand movements are required to transmit a series of dots or dashes.
  • The ability to combine some functions with the use of a tradtional key that is plugged into the electronic keyer.

Often they are hardware devices but they can also be computer or smartphone software applications that provide these and other functions.

Electronic keyers.... They just might save you from carpel-tunnel syndrome!

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Tags: morse code arrl chapter 5 arrl module 11

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